When you view HDR compatible content (Netflix, YouTube, and Amazon do have HDR 4K content now), the contrast and brightness changes on parts of the screen to produce more life-like quality.
With HDR, brights look brighter and darks look darker for a more natural look.
This video explains people who upgraded from 1080p to 4K often did not notice much difference, until HDR was introduced.
For more explanation, here's an article,and a video.
Most other 55-inch TVs with HDR cost $600 and up.
Note, Blu-Ray players and discs do not support HDR.
New "Ultra Blu-Ray" supports HDR, but instead of buying new equipment, stream 4K HDR content from Netflix, Amazon, YouTube, and Vudu.
However with Net Neutrality set to be eliminated in the US on Thursday, unfortunately, the future of 4K HDR streaming video may be in jeopardy for a lot of Americans.
The FCC rules slated to replace Net Neutrality will enable cable companies to tamper with streaming video delivery as a way to generate revenue and unfairly compete for your TV viewing business by slowing competition.
Corporate cable channels and companies will start prioritizing their own content over others, like Verizon did with Netflix before Net Neutrality.
Most Americans have no choice who their home cable Internet company is, so switching to a different Internet provider is not even an option.